Asked on CNN whether he feared that the presumptive GOP nominee would have the same chilling effect on Latinos that conservative Barry Goldwater -- who strongly opposed the Civil Rights Act and who became the GOP nominee in 1964 -- had on African American voters, the Kentucky senator answered in the affirmative.

"I do. I do," McConnell said in the Thursday interview. "And I think the attacks that he's routinely engaged in -- for example, going after Susana Martinez, the Republican governor of New Mexico, the chairman of the Republican Governors' Association -- I think, was a big mistake."

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McConnell pointed to Goldwater's vote against the Civil Rights Act, which Democratic president Lyndon Johnson signed into law in 1964, as a moment that "did define our party, for at least African American voters."

"And it still does today," he added. "That was a complete shift that occurred that year and we've never be able to get them back."

The top Senate Republican also had a few words of advice for the presumptive GOP nominee, urging Trump to be "gracious" in his primary victory.

"What he ought to be doing now is trying to unify the party and I think attacking people once you have won -- it's a time, if you can, to be gracious and to try and bring the party together," McConnell said.

He added, however, that "I don't agree with everything Trump says or does."

Acknowledging that Americans now have "a choice between two unpopular candidates," the Kentucky senator still pushed a vote for Trump, saying he backed the billionaire "because I know for sure that he won't be four more years like the last eight -- he will be a change."